June 28, 2010 at 8:30 am | 1 Comment
What Does it Mean?
In my last blog entry, I talked about oceans on ancient Mars and the evidence for them that planetary scientists are finding in craters on the Red Planet. All the questions about water on Mars really point to a big question about habitability — that is, a world’s capability of sustaining life. There’s a sort of rote list of things that planetary scientists recite when it comes to assessing what a world has to support living beings. It has to have water, warmth, and organic material (food, essentially) for the life to exist. Those things are important for habitability. So, if Mars had water in the distant past, and if it had warmth (from volcanism or heating from its core or if it had an atmosphere that could trap heat), then two of the three conditions for life would have been met. Food — organic material — would be a simple chemical problem to solve. Here on Earth, food for life ranges from the stuff you and I eat every day to the needs of such one-celled beings as bacteria that munch on sulfur. Obviously, early Mars didn’t have gourmet delights that we could eat, but it could well have had plenty of delicacies for one-celled organisms. So, the planet could have been habitable. If we decided to live there in the future, it could still be termed habitable, but only just barely and we’d have to bring along habitats to take advantage of the barely habitable landscape. But, it could be done. And, it likely will be done.
So, we know Earth is habitable (still). And, Mars was and could be. But, what about Venus? You know, that beautifully bright starlike object that’s making a nightly curtain call in our western skies after sunset? Yeah, that one. It’s gorgeous to look at, but if you landed on Venus, you’d fry in an instant, if you weren’t crushed to death first by the hellishly heavy and hot atmosphere. So, how could this volcanic, sulfurous world be habitable? Clearly it isn’t right now, but it may have been in the past.
Scientists at the European Space Agency are operators for the Venus Express orbiter, which has sent back data suggesting very strongly that early Venus could have water — perhaps even an ocean of it — and may have begun its planetary life as a much more Earthlike world. The spacecraft measured the escape of molecules of hydrogen and oxygen from Venus out to space. The rate of escape of hydrogen is roughly twice that of oxygen, and this indicates that water is the source of these escaping materials. There’s also a tracer element called deuterium that also tells scientists that water has been escaping the planet. Deuterium is a heavy form of hydrogen, and it would have more difficulty escaping the planet’s gravitational pull. The presence of large amounts of it in the upper atmosphere of Venus tells us that water has also escaped and left the deuterium behind.
It’s probably unlikely that Venus had Earthlike oceans as shown in the artist’s concept above. If it did have standing water, those pools and/or small oceans could have been formed when comets slammed into the molten surface. If that happened, and if conditions were right, Venus could have been habitable for a short time in its early history. If that’s true, then it begs the question of whether life could have arisen on the planet, only to be snuffed out by Venus’s subsequent changing climate. It’s an interesting idea and one that needs to be explored more.
However, the more likely scenario is that the newborn Venus had no oceans, but sported a very wet atmosphere overlying the molten surface. Over time, sunlight broke the water molecules into hydrogen and oxygen (a process known as “photodissociation”). The newly freed gases fled to space, leaving behind the deuterium. The escape process cooled things down enough, and the surface cooled.
There’s still a lot of “ifs” in these scenarios, but the evidence for water (past and present) is strong, based on the Venus Express data. It’s a good hint that the Venus we see today — hot, arid, miserable, and volcanic — wasn’t always this way. And, it adds more to our store of knowledge about just when a planet can be habitable in its history — provided the conditions are right.
June 26, 2010 at 13:53 pm | Leave a Comment
The Proof is in the Craters
A neat piece of news caught my eye this week — an announcement from the European Space Agency that mineral studies of Mars taken by ESA’s Mars Express mission and NASA’s Mars Reconnaissance Mission show that liquid water was once very widespread on Mars. The evidence lies inside craters spread around the planet, apparently just beneath the surface. It’s in the form of deposits of what are called hydrated silicates — minerals that have been in contact with water sometime in the past.
Lyot Crater (at left) was one of 91 impact craters the missions studied in a search for evidence of water. At least nine of the craters have strong evidence of hydrated silicates. Those minerals form in wet environments either on the surface or underground — and they have now been identified in both the north and south parts of Mars.
Why study craters? Because the impacting objects (asteroid chunks, for example) punched down through the surface of the planet and exposed very ancient surface crust that would have been in contact with water. This means that water was widespread on the Martian surface sometime in the past. This is great news for scientists who are working to understand the role that water played on Mars early in its history. The presence of water means that conditions could have been favorable for life. It doesn’t prove that life existed on Mars — that takes other studies and will very likely require us to visit the planet to prove it for sure. But, the existence of water is a big thing. There are hints of it all over Mars, not just in the hydrated silicates, but in the landforms that seem to be carved by the action of water. This is a fascinating story that is still unfolding for planetary scientists. I, for one, think that we’ll find substantial reservoirs of water (probably locked away in subsurface aquifers and permafrost) on Mars when our first explorers set foot on that dry and dusty desert surface.
June 22, 2010 at 16:54 pm | Leave a Comment
If not, Find out How You Can Get Them
Every night I get to go outside and look up at dark skies. It’s a consequence of where I live — in a rural location devoid of much of the light pollution associated with modern, urban life. As a result, I get to see dark night skies the way our ancestors did — in fact, the way most people on Earth saw the skies until the invention of electric lights and their widespread use outdoors. Amazingly enough, everybody had decent dark skies up until the turn of the 19th century into the 20th. Sure, there were gaslights in some cities, but their effect was nothing like the millions of watts that now get sent skyward by our combined world-wide lighting fixture collection.
Want to learn more about light pollution and its effects on us and the life forms around us? Check out this new three-minute video from McDonald Observatory. It could change the way you view light pollution and the dark skies.
Also, considering joining and supporting the International Dark-Sky Association. This group has done a lot to help people save money and the environment by employing well designed lighting. Their web pages are packed with useful and money-saving ideas to help us use our lighting resources more carefully. In an era where oil spills decorate our news pages and TV broadcasts, and depletion of energy resources is now a household term, looking for ways to use our energy supplies is a wise solution. It also returns to many humans something they haven’t seen for a long time: the beautiful night sky.
June 19, 2010 at 14:07 pm | Leave a Comment
Another Blogging Milestone
The other day I made my one-thousandth post to this blog. I didn’t know this milestone had passed until I logged in today and the helpful counter in the administrative area told me so. What a milestone to achieve with my post about Jupiter and its latest impact! I’m grateful to all my readers who keep coming back. You’re why I write this stuff about the universe!
So, here in post 1,002, what should I write about? Stargazing is always a good topic. There’s nothing like a stroll under the night-time sky to inspire one’s thoughts toward cosmic ideas. We’ve been going out every night to watch the sunset and see who can spot Venus first. It’s there, if you know where to look, and once the skies start to get kinda, sorta dark, the planet is blazing out like a beacon. The good thing about Venus is that you only need clear skies to see it because it’s bright in city skies as well as in the dark countryside. So, I encourage you to check out Venus in the evening.
Venus-gazing reminds me of a phone call we got at the planetarium back when I was a lecturer there. It was from a person who was nearly terrified that the aliens were landing and that we (astronomers) hadn’t told anybody. I asked the caller what made them think the Earth was being invaded and they described how they had been watching this bright light in the western skies each night for a week and how that light got closer to the mountains each night and then disappear. They were sure that the alien ship was landing in the mountains each night. The caller was most upset when I explained that they were seeing the planet Venus set behind the mountains, just as the Sun did each night. Well, I don’t know if they were upset at finding out what they were seeing or embarrassed at not having made the connection between the Sun setting behind the mountains and the planets (and stars) doing the same.
This was years before the Comet Hale-Bopp Heaven’s Gate cult madness and not long before I went back to school and spent some of my grad school years studying comets. We were used to getting phone calls from the public about mysterious lights in the sky, but the imaginative stories some people told never failed to amaze (and sometimes sadden) me.
It seems that when it comes to the sky and understanding what’s in it, somehow some people suspend their common sense, their sense of disbelief, and will swallow anything. I don’t know why that is. I just know that it happens. Which is too bad, because actually studying and understanding how things in the sky work is a very satisfying and fascinating journey. It’s not different from understanding (in general terms) how a car engine works or how a plane works. If you want to know, you probably ask somebody who works on cars, or you find a book on how planes fly. You seek to understand the physical reasons why the car runs and the plane flies.
We wouldn’t tell somebody that a car works by magic or that a plane goes up into the air because of magical spirits that lift it up, would we? So, why, upon seeing a bright light in the sky, did a person jump to an unsupported conclusion that it was a shipload of LGMs on some kind of tour of the planets? Why did the Heaven’s Gaters decide that a known comet was a mothership? They didn’t use common sense — well, let me say that the person who called me at the planetarium at least wanted to know what the light really was. The Heaven’s Gaters didn’t want to know (0r couldn’t let themselves find out) what Comet Hale-Bopp really was.
Certainly stargazing lights some amazing thought-fires in your brain. It certainly does in mine, and I’ve been lucky to be able to share those thoughts with readers since early 2002. It’s been a grand time doing a grand of postings!
June 17, 2010 at 9:17 am | Leave a Comment
Wow! Take a look at this beauty of an image from the European Southern Observatory’s VISTA telescope.
What you’re seeing here is a VISTA view of the galaxy NGC 253, a.k.a. the Sculptor Galaxy, found in the constellation Sculptor (visible in Southern Hemisphere skies). VISTA looked at this galaxy in infrared light, which gave it a great view of the rich collection of dust clouds that thread through the spiral arms of the galaxy. These dust clouds are where star formation takes place. In fact, NGC 253 is a starburst galaxy, one that has undergone waves of star formation. Tracing the dust clouds and bursts of starbirth allows astronomers to understand the formation history of the galaxy and the actions that have shaped it into the barred spiral we see today.
The telescope also was able to see a population of cool, red stars that aren’t very visible (if at all) in optical wavelengths of light (which are the main wavelengths our eyes can see). This is what infrared viewing allows astronomers to do — that is, to peer through the veils of dust that hide the details of the Sculptor Galaxy. Now they can study in deeper detail the myriad of cool red giant stars in the halo that surrounds the galaxy, and measure the composition of some of NGC 253’s small dwarf satellite galaxies. And, they can search for new objects such as globular clusters and ultra-compact dwarf galaxies that would otherwise be invisible without the deep VISTA infrared images.
I remember some years ago when we first started seeing boasts by ground-based observatories that, using new (at the time) technologies such as adaptive optics, astronomers would be able to achieve “near-Hubble” quality observations of such things as the Sculptor Galaxy. Images like this, from a ground-based observatory in Chile, show that it can be done. And, the exciting part is that using observatories like this and the newly improved Hubble Space Telescope, our view of the cosmos is only going to get better!
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Image of Horsehead Nebula: T.A.Rector (NOAO/AURA/NSF) and Hubble Heritage Team (STScI/AURA/NASA)
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